Belt tensioners are generally well known devices used in various belt-drive systems. The tensioner applies a constant belt-tensioning force, which compensates for increases in belt length due to wear and other factors. A common type of belt tensioner comprises a base and a pivot structure eccentrically mounted on the base. The pivot structure has a belt-engaging pulley journalled thereto. A torsion spring is connected between the base and pivot arm to bias the pivot arm and thereby impart a load on a belt.
Various techniques are used to install timing belt tensioners on engines. One of the most commonly used techniques is to use an eccentric adjusting member that forms part of the base. The eccentric adjusting member rotates around a mounting bolt and thereby moves the pivot arm toward or away from the belt. A known installation procedure includes mounting the tensioner on the engine with the eccentric member at the end of range away from the belt, routing the belt into the drive system, rotating the eccentric member towards the belt until the tensioner reaches the nominal operating position, and locking the tensioner with the mounting bolt.
Representative of the art is U.S. Pat. No. 7,285,065 which discloses a belt tensioner for tensioning the belt of a belt drive system includes an eccentric adjusting member, a pivot structure eccentrically mounted on the adjusting member for pivoting around the adjusting member, a belt-tensioning pulley mounted to rotate on the pivot structure, a biasing member that resiliently biases the pivot structure in a belt-tightening direction, and a coupling structure. The coupling structure temporarily couples the pivot structure to the adjusting member to pivot with it during a belt installation procedure, and the configuration keeps the coupling structure unloaded except for a limited period of time during the installation procedure such that the coupling structure can be installed and removed easily. The tensioner is rendered operative after the pivot structure is uncoupled from the adjusting member, thus allowing the pivot structure to pivot with respect to the adjusting member.
What is needed is a tensioner having a rotary member rotationally engaged with the pivot arm, the rotary member in a first position allows rotation of the adjusting member about the fastener, and upon rotation of the rotary member to a second position the rotary member limits movement of the pivot arm in a predetermined range with respect to the adjusting member.